1. Field of the Invention
The present invention relates to the field of network intermediate devices, and more particularly to high-performance switches for routing data in computer networks.
2. Description of Related Art
Network intermediate systems for interconnecting networks include various classes of devices, including bridges, routers and switches. Systems for the interconnection of multiple networks encounter a variety of problems, including the diversity of network protocols executed in the networks to be interconnected, the high bandwidth required in order to handle the convergence of data from the interconnected networks at one place, and the complexity of the systems being designed to handle these problems. As the bandwidth of local area network protocols increases, with the development of so-called asynchronous transfer mode ("ATM"), 100 Megabit per second Ethernet standards, and proposals for gigabit per second Ethernet standards, the problems encountered at network intermediate systems are being multiplied.
One technique which has been the subject of significant research for increasing the throughput of networks is known as the so-called atomic LAN. The atomic LAN is described for example in Cohen, et al., "ATOMIC: A Low-Cost, Very High-Speed, Local Communication Architecture", 1993 International Conference on Parallel Processing. There is a significant amount of published information about the atomic LAN technology. Felderman, et al. "ATOMIC: A High-Speed Local Communication Architecture", Journal of High Speed Networks, Vol. 1, 1994, pp. 1-28; Cohen, et al., "ATOMIC: A Local Communication Network Created Through Repeated Application of Multicomputing Components", DARPA Contract No. DABT63-91-C-001, Oct. 1, 1992; Cohen et al., "The Use of Message-Based Multicomputer Components to Construct Gigabyte Networks"; DARPA Contract No. DABT63-91-C-001, published Jun. 1, 1992; Finn, "An Integration of Network Communications with Workstation Architecture", ACM, A Computer Communication Review, October 1991; Cohen et al. "ATOMIC: Low-cost, Very-High-Speed LAN", DARPA Contract No. DABT63-91-C-001 (publication date unknown, downloaded from Internet on or about May 10, 1996).
The atomic LAN is built by repeating simple four port switch integrated circuits in the end stations, based on the well known Mosaic architecture created at the California Institute of Technology. These integrated circuits at the end stations are interconnected in a mesh arrangement to produce a large pool of bandwidth that can cross many ports. The links that interconnect the switches run at 500 megabits per second. Frames are routed among the end stations of the network using a differential source route code adapted for the mesh. One or more end stations in the mesh act "address consultants" to map the mesh and calculate source route codes. All of the links are self timed, and depend on acknowledged signal protocols to coordinate flow across the links to prevent congestion. The routing method for navigating through the mesh, known as "worm hole" routing is designed to reduce the buffering requirements at each node.
The atomic LAN has not achieved commercial application to a significant degree, with an exception possibly in connection with a supercomputer known as Paragon from Intel Corporation of Santa Clara, Calif. Basically it has been only a research demonstration project. Critical limitations of the design include the fact that it is based on grossly non-standard elements which make commercial use impractical. For example, there is no way to interface the switch chips taught according to the atomic LAN project with standard workstations. Each workstation needs a special interface chip to become part of the mesh in order to participate in the LAN. Nonetheless, the ATOMIC LAN project has demonstrated a high throughput and readily extendable architecture for communicating data.
Typical switches and routers in the prior art are based on an architecture requiring a "backplane" having electrical characteristics that are superior to any of the incoming links to be switched. For example, 3Com Corporation of Santa Clara, Calif., produces a product known as NetBuilder2, having a core bus backplane defined which runs at 800 megabits per second. This backplane moves traffic among various local area network external ports.
There are several problems with the backplane approach typical of prior art intermediate systems. First, the backplane must be defined fast enough to handle the largest load that might occur in the intermediate system. Furthermore, the customer must pay for worst case backplane design, regardless of the customer's actual need for the worst case system. Second, the backplane itself is just another communication link. This communication link must be completely supported as a backplane for the network intermediate system, involving intricate and expensive design. The lower volumes for specialized backplane link further increases the cost of network intermediate systems based on the backplane architecture.
In light of the ever increasing complexity and bandwidth requirements of network intermediate systems in commercial settings, it is desirable to apply the atomic LAN principles in practical, easy to implement, and extendable network intermediate systems.